If you’ve ever sent an email to the wrong person, changed your mind after you sent it or forgot to attach a document when you were supposed to, you can now undo it. That’s because Gmail Labs has added an Undo It feature.
…Turn on Undo Send in Gmail Labs under Settings, and you’ll see a new “Undo” link on every sent mail confirmation. Click “Undo,” and we’ll grab the message before it’s sent and take you right back to compose.
What else? Gmail Labs has added in-mail previews for YouTube, Flickr, Picasa, and Yelp. The only thing bad thing about the Undo is that you only have 5 seconds to change your mind…after that the messages is sent. You better be quick on your feet.